The present invention relates to a marine propulsion unit. In particular, it relates to a marine propulsion unit, for example, such as an outboard motor, that can be restarted as soon as possible after the engine has been flooded with water. The present invention also relates to a method of purging a marine propulsion unit that has been flooded with water.
A propulsion unit, such as an internal combustion engine, for a land vehicle is normally not designed in any way for contact with, or immersion in, a body of water. Should such immersion occur as a result of an accident, the engine will stop, become flooded with water, and will need specialist attention before it can be restarted.
It is not unknown for boats fitted with small motors, such as outboard motors, to capsize. This can happen, for example, on a rescue mission, if the boat is swamped by breakers when the boat is working close in shore. Alternatively, when a rescue vessel is approaching another vessel, it is possible for waves to be re-directed by the vessel that requires rescue and these can swamp the rescue vessel. Furthermore, when a rescue vessel is launched into heavy seas it is possible for the boat to be capsized upon launch. When the vessel capsizes the motor will be submerged, and water will flood into the engine.
Even in the case of a vessel provided with a self-righting capability, the engine is generally flooded with water by the time the vessel has righted itself. Water will inevitably enter the engine, even though mercury gravity switches are provided to switch off the engine once a predetermined angle of roll is reached.
There have been attempts to provide water-proof internal combustion engines, for vehicles required to have full on-land/in-water capability such as tanks. A fully waterproofed engine is, however, expensive. Furthermore, maintenance of such engines is complicated, since great care must be taken during maintenance if the waterproofing is to be maintained.
The present invention, therefore, does not aim to prevent ingress of water into a marine propulsion unit. Instead, it is directed to an engine that can be restarted as soon as possible after it has been flooded with water.
It is known to provide a marine propulsion unit with an openable drain port, to allow water to be drained after the vessel has been righted. However, when an engine is flooded, water will enter all parts of the engine and in particular tends to lodge in the spark plugs. The provision of a drain port in the propulsion unit will not assist in removing water trapped in the spark plugs, and the water trapped in the spark plugs will make it impossible to achieve ignition and restart the propulsion unit.
For example, European Patent EP-B-0 219 278 describes a carburettor fitted with a drainage system. While the drainage system of EP-B-0 219 278 enables water to be drained from the carburettor this is not sufficient to allow the engine to be restarted, the drainage system will not be able to remove water trapped in the spark plugs. It is necessary to remove the spark plugs and either dry them or replace them with new spark plugs before the engine can be restarted. This is very difficult to do in a small boat in heavy seas.
A first aspect of the present invention provides a marine propulsion unit comprising: a cylinder; a combustion chamber extending from a first end of the cylinder; a spark plug disposed within the combustion chamber; and a piston reciprocably movable within the cylinder; wherein the unit further comprises a first aperture, the first aperture being selectively openable independent of the position of the piston within the cylinder, the first aperture being positioned such that, in its open state, movement of the piston causes gas within the propulsion unit to flow over the spark plug thereby to remove water from the spark plug.
When a propulsion unit or the present invention is flooded, the unit can be purged of water simply by opening the first aperture and turning over the unit (either manually or using the starter motor if the unit is provided with one). The movement of the piston will expel water from the unit through the first aperture.
The first aperture of a marine propulsion unit of the present invention is, however, not solely a drain port. In contrast to the prior art drain ports, which are positioned at the lowest point of the engine to provide effective drainage, the first aperture of a propulsion unit of the invention is positioned such that a flow path of gas to the first aperture will pass over the points of the spark plug. Thus, according to the invention, once all water has been expelled, continued movement of the piston will cause gas within the propulsion unit to flow over the contacts of the spark plug. This flow of gas over the spark plug will remove water trapped in the spark plug while the spark plug is in situ. Once enough of the trapped water has been removed from the spark plug to enable ignition to be achieved and so allow the propulsion unit to be restarted, the first aperture is closed. The propulsion unit can then be restarted.
The present invention thus provides a post-immersion restart system that does not require the spark plug to be removed for drying or replacement. Since there is no need to remove the spark plug, the present invention makes restarting much faster, and also much easier to carry out.
The first aperture is preferably positioned to maximise the flow of gas over the spark plug when the first aperture is open, as far as the structural constraints of the engine allow this. This minimises the time taken to remove trapped water from the spark plug.
In a preferred embodiment of the invention, the propulsion unit further comprises an openable second aperture, the second aperture being positioned such that, in its open state, movement of the cylinder causes fluid within the propulsion unit to pass out of the propulsion unit through the second aperture.
Providing the second aperture enables the time needed to purge the propulsion unit to be reduced. Water in the propulsion unit can be expelled through the second aperture, and will not be transferred to the combustion chamber and come into contact with the spark plug.
The second aperture is preferably disposed at substantially the most effective drainage point of the marine propulsion unit, in order to provide the most efficient drainage.
A second aspect of the invention provides an outboard motor comprising a marine propulsion unit as defined above.
A third aspect of the present invention provides a method of determining the location of the first aperture of a marine propulsion unit of the type defined above.
A fourth aspect of the present invention provides a method of purging a marine propulsion unit as defined in claim 18.
A fifth aspect of the present invention provides a method of re-starting a marine propulsion unit as defined in claim 22.
A sixth aspect of the present invention provides a method of starting a marine propulsion unit as defined in claim 23.
Further preferred features of the invention are set out in the other dependent claims.